Field of the Invention
The present disclosure relates to a method for manufacturing an optical circuit board having a reflection surface configured to redirect optical signals.
Description of the Related Art
FIG. 5 shows a conventional optical circuit board B configured to mount an electronic component D thereon. The conventional optical circuit board B includes a wiring board 20 and an optical waveguide 21. This type of conventional optical circuit board B is disclosed in, for example, Japanese Unexamined Patent Publication No. 2005-99514.
The wiring board 20 includes an insulating layer 22 and a wiring conductor 23. The insulating layer 22 is provided with through holes 24. The wiring conductor 23 is formed on upper and lower surfaces of the insulating layer 22 and inside the through holes 24. An electronic component connection pad 25 composed of apart of the wiring conductor 23 is formed on the upper surface of the insulating layer 22. An electronic component connection pad 25 is configured to mount the electronic component D thereon. An external connection pad 26 composed of a part of the wiring conductor 23 is formed on the lower surface of the insulating layer 22. The external connection pad 26 is configured to have a wiring conductor of an external circuit board connected thereto.
The optical waveguide 21 is disposed on the wiring board 20. The optical waveguide 21 is formed of a lower clad layer 21a, a core 21b, and an upper clad layer 21c. The optical waveguide 21 is configured to receive optical signals transmitted thereto. The lower clad layer 21a and the upper clad layer 21c that constitute the optical waveguide 21 are composed of a planar insulating layer. The core 21b has a slender band shape and a rectangular cross section. The lower clad layer 21a and the upper clad layer 21c surround the core 21b while being in close contact with surfaces of the core 21b. The core 21b further has a reflection surface M on one end thereof. The reflection surface M is constituted by a cut surface that is perpendicular to an extension direction of the core 21b and has a predetermined angle with respect to the upper surface of the wiring board 20. Transmission and receiving of optical signals between the optical waveguide 21 and the electronic component D are performed through the reflection surface M.
A conventional method for manufacturing an optical circuit board is described below with reference to FIGS. 6 and 7. The same parts as those in FIG. 5 are labeled with the same reference numerals.
As shown in FIG. 6A, the insulating layer 22 provided with a plurality of the through holes 24 is prepared. The insulating layer 22 is formed by impregnating, for example, an epoxy resin and a bismaleimide triazine resin into a glass cloth, followed by thermal curing. Subsequently, as shown in FIG. 6B, the wiring board 20 is formed by depositing the wiring conductor 23 onto the upper and lower surfaces of the insulating layer 22 and onto the inside of the through holes 24.
As shown in FIG. 6C, the lower clad layer 21a is subsequently formed on the upper surface of the wiring board 20. As shown in FIG. 6D, the core 21b is subsequently formed on the upper surface of the lower clad layer 21a. As shown in FIG. 7E, the upper clad layer 21c is subsequently formed on the upper surface of the core 21b. The optical waveguide 21 is thus formed.
Finally, as shown in FIG. 7F, the core 21b is cut by causing a blade to cut into the core 21b from immediately above the optical waveguide 21. Thus, the conventional optical circuit board B as shown in FIG. 5 is formed by forming the reflection surface M constituted by the cut surface that is perpendicular to the extension direction of the core 21b and has the predetermined angle with respect to the upper surface of the wiring board 20. When forming the reflection surface M, alignment between a central axis in the extension direction of the core 21b and a central position of the reaction surface B is achieved in advance. This makes it possible to accurately perform the transmission and receiving of optical signals between the optical waveguide 21 and the electronic component D. As used herein, the term “central position of the reflection surface M” denotes a position at which a pair of diagonals of the rectangular reflection surface M intersect.
When the optical circuit board B is formed by the conventional manufacturing method, the optical waveguide 21 configured to have the reflection surface M formed thereon is formed on the upper side of the wiring board 20. In some cases, the wiring board 20 may already be subjected to warping due to a thermal history during the manufacturing. The occurrence of warping makes it difficult to accurately cause the blade to cut into a predetermined position of the core 21b when cutting the core 21b with the blade in order to form the reflection surface M. It is therefore difficult to achieve alignment between the central axis in the extension direction of the core 21b and the central position of the reflection surface M. It is consequently difficult to accurately perform the transmission and receiving of optical signals between the optical waveguide 21 and the electronic component D.